Four rabid bats have been found so far this year in the Santa Clarita Valley, and one dog had to be euthanized because it was carrying one of the bats in its mouth, a county Health Department official said Friday.

The number of rabid bats found countywide — 12 so far in 2011 — was up from the eight to 10 usually found in a year, according to a county Public Health Department website.

The reason for the increase was not known, said Dr. Karen Ehnert, acting director for the veterinary public health and rabies control program for the Los Angeles County Department of Public Health.

But the Santa Clarita Valley is a favored environment for the flying mammals, Ehnert said.

“There are large colonies of bats, especially under bridges in river areas,” Ehnert said. They can also hide in attics or under roof tiles.

A typical bat eats about 100 mosquitoes a night, which helps cut down on the spread of West Nile virus, she said.

In Newhall, a dead rabid bat was found on a backyard lawn, and in Saugus, a live rabid bat was found during the day in a parking lot.

Within Santa Clarita city limits, a live rabid bat was found in a swimming pool, and a dead rabid bat was found in a dog's mouth, according to Ehnert.

The dog was not up to date on its rabies vaccination, so its owners decided to euthanize it, Ehnert said.